ASP.Net/Language Basics/If Statement

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If else Demo (C#)

   <source lang="csharp">

<%@ Page Language="C#" %> <script runat="server"> 

   void page_Load()
   {
        if(Page.IsPostBack)
        {
            if(chkIsMember.Checked==true){
                lblOut.Text = "Members get a free ticket";
                lblOut.BackColor=System.Drawing.Color.LightPink;
            }
            else if(Convert.ToInt32(txtAge.Text)<=18) {
                lblOut.Text = "Students get a free ticket";
                lblOut.BackColor=System.Drawing.Color.LightPink;
            }else {
                lblOut.Text = "Price is 500";
                lblOut.BackColor=System.Drawing.Color.LightSeaGreen;
            }
        }
   }

</script> <html> <head> </head> <body> 

   

   <form runat="server">
       Please enter your age 
       <asp:TextBox id="txtAge" runat="server"></asp:TextBox>
       

       Are you a member? 
       <asp:CheckBox id="chkIsMember" runat="server"></asp:CheckBox>
       <asp:Button id="Button1" runat="server" Text="Submit"></asp:Button>
       

       <asp:Label id="lblOut" runat="server"></asp:Label>
       

   </form>

</body> </html> 

      </source>


If statement the check the input value from asp:TextBox (VB.net)

   <source lang="csharp">

<%@ Page Language="VB" %> <script runat="server"> 

   Sub Reset()
   
     Textbox1.Text = ""
     Textbox2.Text = "0"
   
   End Sub
   
   Sub Page_Load(sender As Object, e As EventArgs)
   
     If Not Page.IsPostback
       Reset()
     End If
   
   End Sub
   
   Sub btnSubmit_Click(sender As Object, e As EventArgs)
   
     If cint(textbox2.text) < 20 Then
   
       label1.text = "Hi " & textbox1.text & ", you are " & textbox2.text & ", which is young!"
   
     Else If cint(textbox2.text) < 40 Then
     
       label1.text = "Hi " & textbox1.text & ", you are " & textbox2.text & ", which means you"re middle-aged!"
   
     Else 
   
       label1.text = "Hi " & textbox1.text & ", you"re old!"
   
     End If
   
   End Sub
   
   Sub btnReset_Click(sender As Object, e As EventArgs)
   
     Reset()
   
   End Sub

</script> <html> <head> </head> <body> 

   <form runat="server">

Enter your name: <asp:TextBox id="TextBox1" runat="server"></asp:TextBox>

Enter you age: <asp:TextBox id="TextBox2" runat="server"></asp:TextBox>

<asp:Button id="btnSubmit" onclick="btnSubmit_Click" runat="server" Text="Submit"></asp:Button>   <asp:Button id="btnReset" onclick="btnReset_Click" runat="server" Text="Reset"></asp:Button>

<asp:Label id="Label1" runat="server"></asp:Label> 

   </form>

</body> </html> 

      </source>


If then Demo (C#)

   <source lang="csharp">

<script language="C#" runat="server"> void Page_Load() { 

 int intNumber, intGuess;
 Random r = new Random();
 intNumber = Convert.ToInt32(r.Next(10)) + 1;
 if (Page.IsPostBack) {
   intGuess = Convert.ToInt32(Guess.SelectedItem.Value);
  
   if (intGuess > intNumber) {
      Message.Text = "

Guess is too high
Try again, it was " 
      + intNumber;
   }
   if (intGuess < intNumber) {
      Message.Text = "

Guess is too low
Try again, it was " 
      + intNumber;
   }
   if (intGuess == intNumber) {
      Message.Text = "

Guess is correct!";
   }
 }

} </script> <html> <head></head> <body> <form runat="server"> 

 Guess?
 <asp:dropdownlist id="Guess" runat="server">
   <asp:listitem>1</asp:listitem>
   <asp:listitem>2</asp:listitem>
   <asp:listitem>3</asp:listitem>
   <asp:listitem>4</asp:listitem>
   <asp:listitem>5</asp:listitem>
   <asp:listitem>6</asp:listitem>
   <asp:listitem>7</asp:listitem>
   <asp:listitem>8</asp:listitem>
   <asp:listitem>9</asp:listitem>
   <asp:listitem>10</asp:listitem>
</asp:dropdownlist>
 

 
 
 <input type="submit" value="Submit guess">
 <asp:label id="Message" runat="server"/>

</form> </body> </html> 

      </source>


Multiple conditions in If statement (VB.net)

   <source lang="csharp">

<%@ Page Language="VB" %> <script runat="server"> 

   Sub Calendar1_SelectionChanged(sender As Object, e As EventArgs)
     If Day (Calendar1.SelectedDate) = 13 And Calendar1.SelectedDate.DayOfWeek = 5 Then
       Label1.Text = "Careful! Friday 13th is an unlucky day for some people!"
     Else
       Label1.Text = "It"s just another day in life..."
     End If
   End Sub

</script> <html> <head> </head> <body> 

   <form runat="server">

Please select a date:

<asp:Calendar id="Calendar1" runat="server" OnSelectionChanged="Calendar1_SelectionChanged"></asp:Calendar>

<asp:Label id="Label1" runat="server"></asp:Label> 

   </form>

</body> </html> 

      </source>


Nested if statement (C#)

   <source lang="csharp">

<script language="C#" runat="server"> void Page_Load() { 

 int intNumber, intGuess;
 Random r = new Random();
 intNumber = Convert.ToInt32(r.Next(10)) + 1;
 if (Page.IsPostBack) {
   intGuess = Convert.ToInt32(Guess.SelectedItem.Value);
  
   if (intGuess > intNumber) {
      Message.Text = "

Guess is too high
Try again, it was " 
      + intNumber;
   }
   if (intGuess < intNumber) {
      Message.Text = "

Guess is too low
Try again, it was " 
      + intNumber;
   }
   if (intGuess == intNumber) {
      Message.Text = "

Guess is correct!";
   }
 }

} </script> <html> <head></head> <body> <form runat="server"> 

 What number am I thinking of?
 <asp:dropdownlist id="Guess" runat="server">
   <asp:listitem>1</asp:listitem>
   <asp:listitem>2</asp:listitem>
   <asp:listitem>3</asp:listitem>
   <asp:listitem>4</asp:listitem>
   <asp:listitem>5</asp:listitem>
   <asp:listitem>6</asp:listitem>
   <asp:listitem>7</asp:listitem>
   <asp:listitem>8</asp:listitem>
   <asp:listitem>9</asp:listitem>
   <asp:listitem>10</asp:listitem>
</asp:dropdownlist>
 

 
 
 <input type="submit" value="Submit guess">
 <asp:label id="Message" runat="server"/>

</form> </body> </html> 

      </source>


Nested if statement (VB.net)

   <source lang="csharp">

<script language="vb" runat="server"> Sub Page_Load() 

 Dim theNumber As Integer
 Dim theGuess As Integer
 theNumber = int(10 * rnd) + 1
 If Page.IsPostBack Then
   theGuess = Guess.SelectedItem.Value
   If theGuess > theNumber then
     Message.Text = "

Guess is too high
Try again ?it was " _
     & theNumber
   End If
   If theGuess < theNumber then
     Message.Text = "

Guess is too low
Try again ?it was " _
     & theNumber
   End If
   If theGuess = theNumber then
     Message.Text = "

Guess is correct!"
   End If
 End If

End Sub </script> <html> <head></head> <body> <form runat="server"> 

 What number am I thinking of?
 <asp:dropdownlist id="Guess" runat="server">
   <asp:listitem>1</asp:listitem>
   <asp:listitem>2</asp:listitem>
   <asp:listitem>3</asp:listitem>
   <asp:listitem>4</asp:listitem>
   <asp:listitem>5</asp:listitem>
   <asp:listitem>6</asp:listitem>
   <asp:listitem>7</asp:listitem>
   <asp:listitem>8</asp:listitem>
   <asp:listitem>9</asp:listitem>
   <asp:listitem>10</asp:listitem>
 </asp:dropdownlist>
 

 
 
 <input type="submit" value="Submit guess">
 <asp:label id="message" runat="server"/>

</form> </body> </html> 

      </source>
Источник — «http://nfex.ru/index.php?title=ASP.Net/Language_Basics/If_Statement&oldid=2206»